Step 1

Place the raspberries, strawberries, lemon, vanilla bean, and honey in a heatproof bowl over a pan of simmering water. Cook until berries have released most of their juices, about 12 minutes.

Step 2

Strain mixture through a fine sieve, pressing gently with the back of a spoon. Discard the solids. Cool completely. Mixture will keep for one week in the refrigerator.

Step 3

To serve: Pour 1/4 cup syrup into 4 ice-filled glasses. Top each with 1 cup seltzer. Serve with lemon wedges.